Saturday, February 19, 2011

More Catapults

A few days ago I shared here about our free-form experiments with small hand-made catapults, launching those wiffle-style practice golf balls. In that post I mentioned we'd be following up that session with a more "systematic exploration," although at the time I wasn't sure what that meant, but now I do. Also, several people wrote asking for advice on how to build their own catapults, which I'll try to provide at the bottom of this post.

When the Pre-K kids arrived on Tuesday, they found their blue rug lined with masking tape of various colors, pink, purple, red, light blue, black and green (which is camouflaged in this photo, but it's there, I promise). There was a lot of speculation about why there were tape lines on the rug and we used them to sort ourselves into various categories while waiting for everyone to finish up with their lunch, which is how we start every Pre-K day.

First we each sat on our "favorite color," taking note of which color had the most advocates. There was some competitive cheering about whose color "won," an instinct I, for better or worse, quashed by saying, "Hey, this is science, everybody wins in science." We then sorted by age, discovering that we were all either 4 or 5, although Isak pointed out that there are 3-year-olds who would be sitting on the red line if the 3-year-olds were in class that day. Finally, we tried to sort ourselves by what we most want to be doing with our bodies during circle time. The pink line was for jumping up and down, the purple line for simply standing, the red for kneeling, the light blue for sitting, and the black and green for lying down. Almost everyone chose either the pink line or the black and green zone. I was inclined to trying running our circle time with all those options in force, but it became evident that some of the kids were incapable of jumping up and down without also making motor sounds with their mouths, which made it impossible for us to hear each other, so we wound up just sitting where ever we wanted as we proceeded to the actual reason I'd put lines on the rug.

I pointed out that there was a paper on the easel with matching tape lines, pink, purple, red, light blue, black and green, only these were on a vertical plane as opposed to a horizontal one. I saw several of them confirming this assertion with their own eyes. I then informed them that we were going to be dividing into teams to use catapults again, which was met with enthusiastic cheering, but this time we were going to be trying to launch several different "projectiles" to see which went the farthest: paper, rubber duckies, candy hearts, puff balls, and ping pong balls.

Instead of the higgledy-piggledy method from last week, this time our teams lined up along the edge of the rug closest to the pink line and all aimed in the same direction. They then launched one projectile at a time to see how far it went, which we marked on the tape-lined paper (I didn't use the word "chart" or "graph," I'm not sure why -- a missed opportunity, I think, upon reflection).

We then put away the catapults and analyzed our data. It's a little hard to make out here, but every team found the ping pong balls traveled the greatest distance. The sheets of paper, on the other hand went almost nowhere until we wadded them up, which caused most of them to wind up in the purple-red range. The rubber duckies were universally disappointing. Lachlan speculated that the problem was that they were too heavy, a theory with which we all agreed. Three of the teams had their puffballs travel to the red line, while the fourth team barely managed the pink line. Charlie B. felt this had to do with "doing the catapult wrong." His teammates nodded agreement. The biggest discrepancy was the distances covered by the candy hearts. Two of the teams landed in the pink-purple range, while one team's heart went across the black line and another passed the green line. After some discussion it was determined that in these two cases, the hearts had landed on their sides and rolled most of the distance.

A satisfying, systematic exploration, lacking only the teacher's evocation of the words "chart" or "graph." Oh well, they'll hear those words some other time.

Making Your Own Classroom Catapult
I made these catapults 4 years ago when my daughter was in the 4th grade. (If you click on the photos to view them full sized, you should be able to make out more of the construction details.)

Her school's Fall Festival had a medieval theme and the 4th grade class wanted to knock down cardboard block walls with catapults. For that, I built some amazing (if I do say so myself) monstrosities using bungee cords that could launch a tennis ball at great velocity. It was big fun, but when I brought them into the preschool it became abundantly evident that they were far too powerful for the younger set, so I wound up giving them away to families who, apparently, were more bruise tolerant. I then made these small rubber band powered ones for Woodland Park use.

They're made from scrap plywood, glue, small nails, and a bottle cap. I'm sure there are better designs out there, but I just used a piece of wood about a foot long and maybe 4 inches wide as the base.

I then glued the sides on with your basic wood glue, using C-clamps to makes sure it would hold under the tension of repeated catapulting. I'm pretty sure I drove a few small nails along the bottom as well for good measure.

Once the glue was dry, I installed the lever part by drilling holes through the side boards, threading a dowel through one hole, then through a hole in the base of the lever, then out the other side. I made sure the hole I drilled in the lever was a tight fit for the dowel and augmented it with more glue.

I then nailed on the "stop bar" piece. This is an important aspect of a catapult. Without it, the machine will just slam your projectiles right into the ground.

If you click on the top photo here to enlarge it, you'll see how I then added a small eye-screw about halfway up the back of the lever, then drove two small nails into the tops of the side boards, bending them forward. I hooked a long rubber band on one nail, threaded it through the eye-screw, then hooked it on the other side. (The kids got really good at repairing this part of their catapults, Isak even dismantling his team's intentionally to prove to himself he could put it back together.)

Finally, I used a large bottle cap on the end of the lever to hold the projectiles. It might have been better to use something deeper.

I've never tried a tutorial before. I hope this doesn't just confuse you more.

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Betsy said...

Thanks Tom! My Pre-K class had great fun making and using the clothes-pin catapults, but they took them home. I think I have to make a few of these for classroom use!

child central station said...

We went "catapult crazy" last summer/fall. My little ones had a blast! We even hung hula hoops from the ceiling to allow the children to try to send objects flying through the hoops! We used the clothespin ones inside and a much larger bungee cord "ogre" catapult outside. I'm sure we'll be trying out this style soon. There is a great book out there called Backyard Ballistics that has great tutorials and instructions on how to make a potato cannon with pvc pipe!

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Barbara Zaborowski said...

Hi Tom,

I noticed that the lever on your catapult appears to stop just past straight upright (or possibly at upright.) If you want more distance (and I realize that that's a big "if"), the lever should stop just SHORT of upright. This can be accomplished by adding another stop bar on top of the sides. Then the projectile would be launched both outward and upward (slightly).
Either way, great fun! I so enjoy your blog.

S. Krajicek said...


Anonymous said...

This is a great activity for kids. Launching stuff into the air is cool. Here is an Instructable I did for a backyard catapult that my five year old loved:

Brent Geppert

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